The present invention relates broadly to the field of ultrasonically testing of turbine rotors and more particularly, to a programmed microprocessor-based electronic controller for adaptively coordinating the ultrasonic testing operations of an ultrasonic tester and associated drive unit in a selected one of a plurality of control modes, each control mode conducted in accordance with observable test data and anomaly indications generated from the ultrasonic tester and drive unit during testing operations.
Ultrasonic testing of turbine rotor shafts is primarily performed as a form of preventive maintenance to uncover imperfections in the rotor material such as slight fractures, differences in crystalline structure and even small inclusions from a piece of slag or some other nonhomogeneous matter, for example, that is, anything which may reflect propagated ultrasonic waves differently from within the rotor material. Normally, these types of imperfections are not visible upon inspection of a turbine rotor under test. Ultrasonic testing of the turbine rotors may be conducted after construction at the assembly plant and during planned shutdown maintenance intervals for a turbine system at a user's facility.
Generally, during an ultrasonic rotor test, one or more crystal transducers, usually attached arcuately about one end of a mechanical arm, are axially positioned and angularly oriented through the bore of a turbine rotor under test. The axial and angular positioning of the crystal transducers is generally brought about by a motor drive unit which indexes the one end of the mechanical arm through the rotor bore at predetermined increments, say one-fourth inch, for example, while simultaneously rotating the crystals about the longitudinal axis of the mechanical arm in an arc of approximately 375.degree. with each incremental movement. Working independently of the motor drive unit is an ultrasonic tester which is electrically coupled to the crystal transducers to pulse them at periodic intervals causing ultrasonic signals to be propagated into the turbine rotor material and to receive from them, the back reflected echo signals associated with each ultrasonic pulse transmission. Some ultrasonic testers are of the type which normalize and linearize the received echo signals with respect to predetermined time intervals within the reception time between transmitted ultrasonic pulses. The time delay between the pulse transmission and reception of the back reflected echo signal is representative of the radial distance or depth location within the turbine rotor material thickness which is causing the reflection and the amplitude level of the back reflected echo signal is a measure of the size of the potential imperfection. In these type testers, the conditioned amplitude level of the received echo signals may be compared to an adjustable threshold level so as to render an anomaly indication corresponding to the times when the conditioned echo signals exceed the adjusted threshold level. Normally, the conditioned reflected signals are displayed on the screen of a CRT on a trace which is usually synchronized to the ultrasonic signal transmissions and time scaled in relation to the radial dimensions of the turbine rotor material thickness.
Typically, the ultrasonic testing of turbine rotors is conducted manually by an operator who initially calibrates the motor drive unit and ultrasonic tester according to well-known calibration procedures. Once this is accomplished, the operator adjusts the motor drive unit to index the mechanical arm and crystal transducers through the rotor bore in predetermined increments and adjusts the ultrasonic tester to pulse the crystal transducers with a periodicity adequate for the range of rotor material thickness and sufficient to provide for a visible display of the conditioned echo signals on the screen of the CRT. Thereafter, the motor drive unit indexes the mechanical arm through the rotor bore until an anomaly indication is generated by the ultrasonic tester at which time the drive motor is stopped. Normally, there is a time delay between the detection of the anomaly condition and the stopping of the drive motor. Consequently, the operator must manually adjust the drive motor to maximize the amplitude level of the conditioned reflected echo signal as displayed on the screen of the CRT so as to identify the maximum amplitude and exact location of the potential imperfections in the rotor material. This adjustment is a very tedious and time consuming portion of the ultrasonic testing process.
Once the operator feels that the conditioned echo signal has been maximized, he records its amplitude level and representative depth within the rotor thickness as a function of time with respect to the synchronized ultrasonic transmission pulses. The axial positions and angular orientation of the crystal transducers within the rotor bore are also recorded in addition to the crystal transducer channel which is receiving the maximized anomaly reflection. These testing steps are repeated and testing data recorded for each anomaly condition detected by the ultrasonic tester. A complete ultrasonic test of a typical rotor assembly takes approximately 12 to 20 hours using the procedure described above. When the ultrasonic testing is performed at a user's facility, the handwritten tabulated test data is mailed to a central quality control center for evaluation. Results of the evaluation are provided by return mail.
It is evident that the present ultrasonic testing apparatus for identifying potential imperfections in turbine rotors requires the constant attention of an operator for operating the equipment and recording the locations and magnitudes of the potential imperfections resulting in anomaly indications. Consequently, at least one operator is tied up for approximately 12-20 hours of testing the turbine rotor. This results not only in a handicap and inefficiency in manpower allocation, but also renders the turbine system unavailable for other maintenance functions, thus extending the planned maintenance shutdown time. One possibility for relieving the time and labors burdens associated with the present ultrasonic testing procedures is to reduce or eliminate the necessity of the operator element during the testing phase by automating the ultrasonic testing procedures. It is felt that an electronically automated ultrasonic system will decrease testing time and free the operator for other maintenance duties, offer more accurate and better tabulated test data with regard to measuring the effective geometric locations and magnitude of the potential imperfections, and may even provide the test results in a transmittable form for telecommunications between a quality control center and the test site to decrease the delay time for receiving the evaluation results identifying the severity of the uncovered anomalies.